1. Field of the Invention
The present invention relates to a medical container stopper and, more particularly, to a medical container stopper for hermetically sealing medical container, particularly a reduced pressure blood collection tube at its opening.
2. Description of the Prior Art
Hard medical containers such as so-called vacuum blood collection tubes or drug bottles are hermetically sealed at their openings in order to maintain internal reduced pressure or to shield the contents from the external atmosphere. For this purpose, a vulcanized butyl rubber stopper is conventionally used. This type of stopper can provide a good hermetic seal. However, as pointed out in Japanese Patent Disclosure No. 58-58057, additives contained in the vulcanized butyl rubber such as sulfur or a vulcanization accelerator elute into blood or drugs. In order to resolve this problem, a stopper made of a polymeric substance other than vulcanized butyl rubber is disclosed in the Japanese Patent Disclosure No. 58-58057 mentioned above. A stopper disclosed in this Disclosure is made of a material comprising 30 to 80% by weight of a butyl rubber and 20 to 70% by weight of a thermoplastic elastomer. The stopper provides an excellent hermetic seal and is free from the problem encountered with vulcanized butyl rubber.
However, the stopper disclosed in Japanese Patent Disclosure No. 58-58057 still poses problems with respect to compression set and gas barrier performance (gas impermeability).